1. Field of the Invention
The present invention relates to an organic semiconductor element having an organic semiconductor film and a method for manufacturing thereof.
2. Description of the Related Art
In recent years, a display device provided with a thin film transistor (hereinafter, a TFT) having a thin film semiconductor has been studied and put into practical use. A high-resolution display device can be achieved since a large number of pixels can be constituted in the display device provided with a TFT. Moreover, the display device provided with a TFT can be operated in low power consumption compared with a CRT. Furthermore, the display device provided with a TFT occupies small space, since a display can be made without using a large-sized display tube like a CRT. Thus, the display device provided with a TFT has been widely used for a display portion of a personal computer, a PDA, a TV, or the like.
A display device which is made thinner, lighter, and more flexible is required in future. However, most of conventional TFTs have been manufactured by using an inorganic semiconductor material such as amorphous silicon or crystalline silicon as a semiconductor film. Therefore, the use of a resin substrate such as a plastic is limited since a processing temperature of 350° C. or more is required for forming a semiconductor film in the case where a TFT is formed by using an inorganic semiconductor material.
In recent years, an organic thin film transistor (hereinafter, an organic TFT) in which an organic semiconductor is used as a semiconductor layer has been studied. An organic TFT has high flexibility since an organic material is used. Moreover, a device using an organic semiconductor can be manufactured at a lower temperature compared with a device using an inorganic semiconductor; thereby a resin material such as a plastic can be used for a substrate. As a result, a lightweight and flexible device can be obtained.
Moreover, as for an organic TFT, it is expected that not only can process such as a printing method, an ink-jetting method, and a vapor deposition method be simplified, but a manufacturing cost of a device can be also suppressed since an inexpensive material for a substrate can be used, and thus it is advantageous in view of the cost.
Moreover, as for an organic TFT manufactured at present, a TFT element in which pentacene is laminated over an SiO2/Si substrate in which only surface cleaning is carried out and over a substrate in which the surface is treated with HMDS after carrying out surface cleaning under the same condition is manufactured. (refer to Non-Patent Document 1: I. Yagi, K. Tsukagoshi, and Y. Aoyagi, “Pentacene FET fabricated on surface treated SiO2/Si substrate”, Proceedings of the 50th Japan Society of Applied Physics Lectures (March 2003), lower section of p. 1418.)
According to the Non-Patent Document 1, as for an organic TFT in which a surface is not treated, preferable TFT characteristic can be obtained in mobility, ON-OFF ratio, or a threshold value only in the case of using an element in which a channel length is long or a channel width is wide.
However, in the case of manufacturing a device using an organic TFT, it is essential to develop an element in which a channel length is short or a channel width is narrow in order to downsize a device.